wasm2c: Add segue option to make exclusive use of the segment register

WebAssembly · Sep 6, 2024 · 8f7a227 · 8f7a227
1 parent c6853eb
commit 8f7a227
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Showing 14 changed files with 209 additions and 55 deletions.
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
@@ -203,7 +203,7 @@ jobs:
     env:
       USE_NINJA: "1"
       WASM2C_CC: "clang"
-      WASM2C_CFLAGS: "-DWASM_RT_USE_MMAP=1 -DWASM_RT_SKIP_SIGNAL_RECOVERY=1 -DWASM_RT_NONCONFORMING_UNCHECKED_STACK_EXHAUSTION=1 -DWASM2C_TEST_EMBEDDER_SIGNAL_HANDLING -DWASM_RT_ALLOW_SEGUE=1 -mfsgsbase -DWASM_RT_SANITY_CHECKS=1 -Wno-pass-failed"
+      WASM2C_CFLAGS: "-DWASM_RT_USE_MMAP=1 -DWASM_RT_SKIP_SIGNAL_RECOVERY=1 -DWASM_RT_NONCONFORMING_UNCHECKED_STACK_EXHAUSTION=1 -DWASM2C_TEST_EMBEDDER_SIGNAL_HANDLING -DWASM_RT_ALLOW_SEGUE=1 -DWASM_RT_SEGUE_FREE_SEGMENT=1 -mfsgsbase -DWASM_RT_SANITY_CHECKS=1 -Wno-pass-failed"
     steps:
     - uses: actions/setup-python@v1
       with:

diff --git a/src/c-writer.cc b/src/c-writer.cc
@@ -2449,7 +2449,9 @@ bool CWriter::IsSingleUnsharedMemory() {
 void CWriter::InstallSegueBase(Memory* memory, bool save_old_value) {
   NonIndented([&] { Write("#if WASM_RT_USE_SEGUE", Newline()); });
   if (save_old_value) {
+    NonIndented([&] { Write("#if !WASM_RT_SEGUE_FREE_SEGMENT", Newline()); });
     Write("void* segue_saved_base = wasm_rt_segue_read_base();", Newline());
+    NonIndented([&] { Write("#endif", Newline()); });
   }
   auto primary_memory =
       ExternalInstanceRef(ModuleFieldType::Memory, memory->name);
@@ -2458,7 +2460,9 @@ void CWriter::InstallSegueBase(Memory* memory, bool save_old_value) {
 }
 
 void CWriter::RestoreSegueBase() {
-  NonIndented([&] { Write("#if WASM_RT_USE_SEGUE", Newline()); });
+  NonIndented([&] {
+    Write("#if WASM_RT_USE_SEGUE && !WASM_RT_SEGUE_FREE_SEGMENT", Newline());
+  });
   Write("wasm_rt_segue_write_base(segue_saved_base);", Newline());
   NonIndented([&] { Write("#endif", Newline()); });
 }

diff --git a/src/prebuilt/wasm2c_source_declarations.cc b/src/prebuilt/wasm2c_source_declarations.cc
@@ -115,13 +115,34 @@ R"w2c_template(}
 )w2c_template"
 R"w2c_template(static inline void wasm_rt_segue_write_base(void* base) {
 )w2c_template"
-R"w2c_template(  if (wasm_rt_fsgsbase_inst_supported) {
+R"w2c_template(  bool should_set = true;
+)w2c_template"
+R"w2c_template(#if WASM_RT_SEGUE_FREE_SEGMENT
 )w2c_template"
-R"w2c_template(    __builtin_ia32_wrgsbase64((uintptr_t)base);
+R"w2c_template(  if (wasm_rt_last_segment_val == base) {
+)w2c_template"
+R"w2c_template(    should_set = false;
 )w2c_template"
 R"w2c_template(  } else {
 )w2c_template"
-R"w2c_template(    wasm_rt_syscall_set_segue_base(base);
+R"w2c_template(    wasm_rt_last_segment_val = base;
+)w2c_template"
+R"w2c_template(  }
+)w2c_template"
+R"w2c_template(#endif
+)w2c_template"
+R"w2c_template(
+  if (should_set) {
+)w2c_template"
+R"w2c_template(    if (wasm_rt_fsgsbase_inst_supported) {
+)w2c_template"
+R"w2c_template(      __builtin_ia32_wrgsbase64((uintptr_t)base);
+)w2c_template"
+R"w2c_template(    } else {
+)w2c_template"
+R"w2c_template(      wasm_rt_syscall_set_segue_base(base);
+)w2c_template"
+R"w2c_template(    }
 )w2c_template"
 R"w2c_template(  }
 )w2c_template"

diff --git a/src/template/wasm2c.declarations.c b/src/template/wasm2c.declarations.c
@@ -58,10 +58,21 @@ static inline void* wasm_rt_segue_read_base() {
   }
 }
 static inline void wasm_rt_segue_write_base(void* base) {
-  if (wasm_rt_fsgsbase_inst_supported) {
-    __builtin_ia32_wrgsbase64((uintptr_t)base);
+  bool should_set = true;
+#if WASM_RT_SEGUE_FREE_SEGMENT
+  if (wasm_rt_last_segment_val == base) {
+    should_set = false;
   } else {
-    wasm_rt_syscall_set_segue_base(base);
+    wasm_rt_last_segment_val = base;
+  }
+#endif
+
+  if (should_set) {
+    if (wasm_rt_fsgsbase_inst_supported) {
+      __builtin_ia32_wrgsbase64((uintptr_t)base);
+    } else {
+      wasm_rt_syscall_set_segue_base(base);
+    }
   }
 }
 #define MEM_ADDR_MEMOP(mem, addr, n) ((uint8_t __seg_gs*)(uintptr_t)addr)

diff --git a/test/wasm2c/add.txt b/test/wasm2c/add.txt
@@ -125,10 +125,21 @@ static inline void* wasm_rt_segue_read_base() {
   }
 }
 static inline void wasm_rt_segue_write_base(void* base) {
-  if (wasm_rt_fsgsbase_inst_supported) {
-    __builtin_ia32_wrgsbase64((uintptr_t)base);
+  bool should_set = true;
+#if WASM_RT_SEGUE_FREE_SEGMENT
+  if (wasm_rt_last_segment_val == base) {
+    should_set = false;
   } else {
-    wasm_rt_syscall_set_segue_base(base);
+    wasm_rt_last_segment_val = base;
+  }
+#endif
+
+  if (should_set) {
+    if (wasm_rt_fsgsbase_inst_supported) {
+      __builtin_ia32_wrgsbase64((uintptr_t)base);
+    } else {
+      wasm_rt_syscall_set_segue_base(base);
+    }
   }
 }
 #define MEM_ADDR_MEMOP(mem, addr, n) ((uint8_t __seg_gs*)(uintptr_t)addr)

diff --git a/test/wasm2c/check-imports.txt b/test/wasm2c/check-imports.txt
@@ -149,10 +149,21 @@ static inline void* wasm_rt_segue_read_base() {
   }
 }
 static inline void wasm_rt_segue_write_base(void* base) {
-  if (wasm_rt_fsgsbase_inst_supported) {
-    __builtin_ia32_wrgsbase64((uintptr_t)base);
+  bool should_set = true;
+#if WASM_RT_SEGUE_FREE_SEGMENT
+  if (wasm_rt_last_segment_val == base) {
+    should_set = false;
   } else {
-    wasm_rt_syscall_set_segue_base(base);
+    wasm_rt_last_segment_val = base;
+  }
+#endif
+
+  if (should_set) {
+    if (wasm_rt_fsgsbase_inst_supported) {
+      __builtin_ia32_wrgsbase64((uintptr_t)base);
+    } else {
+      wasm_rt_syscall_set_segue_base(base);
+    }
   }
 }
 #define MEM_ADDR_MEMOP(mem, addr, n) ((uint8_t __seg_gs*)(uintptr_t)addr)
@@ -825,11 +836,13 @@ void wasm2c_test_instantiate(w2c_test* instance, struct w2c_env* w2c_env_instanc
   init_tables(instance);
   init_memories(instance);
 #if WASM_RT_USE_SEGUE
+#if !WASM_RT_SEGUE_FREE_SEGMENT
   void* segue_saved_base = wasm_rt_segue_read_base();
+#endif
   wasm_rt_segue_write_base((*instance->w2c_env_0x5F_linear_memory).data);
 #endif
   init_elem_instances(instance);
-#if WASM_RT_USE_SEGUE
+#if WASM_RT_USE_SEGUE && !WASM_RT_SEGUE_FREE_SEGMENT
   wasm_rt_segue_write_base(segue_saved_base);
 #endif
 }

diff --git a/test/wasm2c/export-names.txt b/test/wasm2c/export-names.txt
@@ -149,10 +149,21 @@ static inline void* wasm_rt_segue_read_base() {
   }
 }
 static inline void wasm_rt_segue_write_base(void* base) {
-  if (wasm_rt_fsgsbase_inst_supported) {
-    __builtin_ia32_wrgsbase64((uintptr_t)base);
+  bool should_set = true;
+#if WASM_RT_SEGUE_FREE_SEGMENT
+  if (wasm_rt_last_segment_val == base) {
+    should_set = false;
   } else {
-    wasm_rt_syscall_set_segue_base(base);
+    wasm_rt_last_segment_val = base;
+  }
+#endif
+
+  if (should_set) {
+    if (wasm_rt_fsgsbase_inst_supported) {
+      __builtin_ia32_wrgsbase64((uintptr_t)base);
+    } else {
+      wasm_rt_syscall_set_segue_base(base);
+    }
   }
 }
 #define MEM_ADDR_MEMOP(mem, addr, n) ((uint8_t __seg_gs*)(uintptr_t)addr)
@@ -796,59 +807,69 @@ static void init_memories(w2c_test* instance) {
 /* export: '' */
 void w2c_test_(w2c_test* instance) {
 #if WASM_RT_USE_SEGUE
+#if !WASM_RT_SEGUE_FREE_SEGMENT
   void* segue_saved_base = wasm_rt_segue_read_base();
+#endif
   wasm_rt_segue_write_base((*instance->w2c_0x5Cmodule_import0x200x2A0x2F).data);
 #endif
   w2c_test__0(instance);
-#if WASM_RT_USE_SEGUE
+#if WASM_RT_USE_SEGUE && !WASM_RT_SEGUE_FREE_SEGMENT
   wasm_rt_segue_write_base(segue_saved_base);
 #endif
 }
 
 /* export: '*\2F' */
 void w2c_test_0x2A0x2F(w2c_test* instance) {
 #if WASM_RT_USE_SEGUE
+#if !WASM_RT_SEGUE_FREE_SEGMENT
   void* segue_saved_base = wasm_rt_segue_read_base();
+#endif
   wasm_rt_segue_write_base((*instance->w2c_0x5Cmodule_import0x200x2A0x2F).data);
 #endif
   w2c_test__0(instance);
-#if WASM_RT_USE_SEGUE
+#if WASM_RT_USE_SEGUE && !WASM_RT_SEGUE_FREE_SEGMENT
   wasm_rt_segue_write_base(segue_saved_base);
 #endif
 }
 
 /* export: '\3F\3F\2F' */
 void w2c_test_0x3F0x3F0x2F(w2c_test* instance) {
 #if WASM_RT_USE_SEGUE
+#if !WASM_RT_SEGUE_FREE_SEGMENT
   void* segue_saved_base = wasm_rt_segue_read_base();
+#endif
   wasm_rt_segue_write_base((*instance->w2c_0x5Cmodule_import0x200x2A0x2F).data);
 #endif
   w2c_test__0(instance);
-#if WASM_RT_USE_SEGUE
+#if WASM_RT_USE_SEGUE && !WASM_RT_SEGUE_FREE_SEGMENT
   wasm_rt_segue_write_base(segue_saved_base);
 #endif
 }
 
 /* export: '\0A' */
 void w2c_test_0x0A(w2c_test* instance) {
 #if WASM_RT_USE_SEGUE
+#if !WASM_RT_SEGUE_FREE_SEGMENT
   void* segue_saved_base = wasm_rt_segue_read_base();
+#endif
   wasm_rt_segue_write_base((*instance->w2c_0x5Cmodule_import0x200x2A0x2F).data);
 #endif
   w2c_test__0(instance);
-#if WASM_RT_USE_SEGUE
+#if WASM_RT_USE_SEGUE && !WASM_RT_SEGUE_FREE_SEGMENT
   wasm_rt_segue_write_base(segue_saved_base);
 #endif
 }
 
 /* export: '\E2\9D\A4\EF\B8\8F' */
 void w2c_test_0xE20x9D0xA40xEF0xB80x8F(w2c_test* instance) {
 #if WASM_RT_USE_SEGUE
+#if !WASM_RT_SEGUE_FREE_SEGMENT
   void* segue_saved_base = wasm_rt_segue_read_base();
+#endif
   wasm_rt_segue_write_base((*instance->w2c_0x5Cmodule_import0x200x2A0x2F).data);
 #endif
   w2c_test__0(instance);
-#if WASM_RT_USE_SEGUE
+#if WASM_RT_USE_SEGUE && !WASM_RT_SEGUE_FREE_SEGMENT
   wasm_rt_segue_write_base(segue_saved_base);
 #endif
 }
@@ -866,10 +887,12 @@ void wasm2c_test_instantiate(w2c_test* instance, struct w2c_0x5Cmodule* w2c_0x5C
   init_instance_import(instance, w2c_0x5Cmodule_instance);
   init_memories(instance);
 #if WASM_RT_USE_SEGUE
+#if !WASM_RT_SEGUE_FREE_SEGMENT
   void* segue_saved_base = wasm_rt_segue_read_base();
+#endif
   wasm_rt_segue_write_base((*instance->w2c_0x5Cmodule_import0x200x2A0x2F).data);
 #endif
-#if WASM_RT_USE_SEGUE
+#if WASM_RT_USE_SEGUE && !WASM_RT_SEGUE_FREE_SEGMENT
   wasm_rt_segue_write_base(segue_saved_base);
 #endif
 }

diff --git a/test/wasm2c/hello.txt b/test/wasm2c/hello.txt
@@ -157,10 +157,21 @@ static inline void* wasm_rt_segue_read_base() {
   }
 }
 static inline void wasm_rt_segue_write_base(void* base) {
-  if (wasm_rt_fsgsbase_inst_supported) {
-    __builtin_ia32_wrgsbase64((uintptr_t)base);
+  bool should_set = true;
+#if WASM_RT_SEGUE_FREE_SEGMENT
+  if (wasm_rt_last_segment_val == base) {
+    should_set = false;
   } else {
-    wasm_rt_syscall_set_segue_base(base);
+    wasm_rt_last_segment_val = base;
+  }
+#endif
+
+  if (should_set) {
+    if (wasm_rt_fsgsbase_inst_supported) {
+      __builtin_ia32_wrgsbase64((uintptr_t)base);
+    } else {
+      wasm_rt_syscall_set_segue_base(base);
+    }
   }
 }
 #define MEM_ADDR_MEMOP(mem, addr, n) ((uint8_t __seg_gs*)(uintptr_t)addr)
@@ -833,11 +844,13 @@ wasm_rt_memory_t* w2c_test_memory(w2c_test* instance) {
 /* export: '_start' */
 void w2c_test_0x5Fstart(w2c_test* instance) {
 #if WASM_RT_USE_SEGUE
+#if !WASM_RT_SEGUE_FREE_SEGMENT
   void* segue_saved_base = wasm_rt_segue_read_base();
+#endif
   wasm_rt_segue_write_base(instance->w2c_memory.data);
 #endif
   w2c_test_0x5Fstart_0(instance);
-#if WASM_RT_USE_SEGUE
+#if WASM_RT_USE_SEGUE && !WASM_RT_SEGUE_FREE_SEGMENT
   wasm_rt_segue_write_base(segue_saved_base);
 #endif
 }
@@ -852,12 +865,14 @@ void wasm2c_test_instantiate(w2c_test* instance, struct w2c_wasi__snapshot__prev
   init_tables(instance);
   init_memories(instance);
 #if WASM_RT_USE_SEGUE
+#if !WASM_RT_SEGUE_FREE_SEGMENT
   void* segue_saved_base = wasm_rt_segue_read_base();
+#endif
   wasm_rt_segue_write_base(instance->w2c_memory.data);
 #endif
   init_elem_instances(instance);
   init_data_instances(instance);
-#if WASM_RT_USE_SEGUE
+#if WASM_RT_USE_SEGUE && !WASM_RT_SEGUE_FREE_SEGMENT
   wasm_rt_segue_write_base(segue_saved_base);
 #endif
 }

diff --git a/test/wasm2c/minimal.txt b/test/wasm2c/minimal.txt
@@ -119,10 +119,21 @@ static inline void* wasm_rt_segue_read_base() {
   }
 }
 static inline void wasm_rt_segue_write_base(void* base) {
-  if (wasm_rt_fsgsbase_inst_supported) {
-    __builtin_ia32_wrgsbase64((uintptr_t)base);
+  bool should_set = true;
+#if WASM_RT_SEGUE_FREE_SEGMENT
+  if (wasm_rt_last_segment_val == base) {
+    should_set = false;
   } else {
-    wasm_rt_syscall_set_segue_base(base);
+    wasm_rt_last_segment_val = base;
+  }
+#endif
+
+  if (should_set) {
+    if (wasm_rt_fsgsbase_inst_supported) {
+      __builtin_ia32_wrgsbase64((uintptr_t)base);
+    } else {
+      wasm_rt_syscall_set_segue_base(base);
+    }
   }
 }
 #define MEM_ADDR_MEMOP(mem, addr, n) ((uint8_t __seg_gs*)(uintptr_t)addr)

diff --git a/test/wasm2c/tail-calls.txt b/test/wasm2c/tail-calls.txt
@@ -149,10 +149,21 @@ static inline void* wasm_rt_segue_read_base() {
   }
 }
 static inline void wasm_rt_segue_write_base(void* base) {
-  if (wasm_rt_fsgsbase_inst_supported) {
-    __builtin_ia32_wrgsbase64((uintptr_t)base);
+  bool should_set = true;
+#if WASM_RT_SEGUE_FREE_SEGMENT
+  if (wasm_rt_last_segment_val == base) {
+    should_set = false;
   } else {
-    wasm_rt_syscall_set_segue_base(base);
+    wasm_rt_last_segment_val = base;
+  }
+#endif
+
+  if (should_set) {
+    if (wasm_rt_fsgsbase_inst_supported) {
+      __builtin_ia32_wrgsbase64((uintptr_t)base);
+    } else {
+      wasm_rt_syscall_set_segue_base(base);
+    }
   }
 }
 #define MEM_ADDR_MEMOP(mem, addr, n) ((uint8_t __seg_gs*)(uintptr_t)addr)